The three-digit telephone number "9-1-1" has been designated as the "Universal Emergency Number," for citizens throughout the United States to request emergency assistance. It is intended as a nationwide telephone number and gives the public fast and easy access to a Public Safety Answering Point (PSAP).

In most areas of North America, citizens have basic or enhanced 9-1-1 service from their landline, or wireline, phones in their homes or workplaces.  Basic 9-1-1 means that when the three-digit number is dialed, a call taker/dispatcher in the local public safety answering point (PSAP), or 9-1-1 center, answers the call.  The emergency and its location are communicated by voice between the caller and the call taker.  In areas serviced by Enhanced 9-1-1, the local 9-1-1 center has equipment and database information that allow the call taker to see the caller's phone number and address on a display.  This lets them quickly dispatch emergency help, even if the caller is unable to communicate where they are or what the emergency is.

At the end of the 20th century, nearly 93% of the population of the United States was covered by some type of 9-1-1 service. Ninety-five percent of that coverage was Enhanced 9-1-1. Approximately 96% of the geographic US is covered by some type of 9-1-1.